Ever wondered just what’s hiding in the various system directories that make up Windows, or why an operating system needs to take up quite so much room? A post at the Engineering Windows 7 blog reveals some of the secrets of Windows’ internal structure (including how some files get counted twice if you try and do a right-click directory size measurement). It also explains why deleting the apparently space-hogging WinSxS directory is a bad idea, which is a useful addition to our existing collection of Vista performance-tweaking myths.